Solid state starters/controllers have found widespread use for controlling application of power to an AC induction motor. The conventional starter/controller, referred to hereinafter as simply a starter or a controller, uses solid state switches for controlling application of AC line voltage to the motor. The switches may be thyristors such as silicon controlled rectifiers (SCRs) or triacs.
One application for a motor controller is as an elevator starter. The elevator starter may be used to drive a pump for an hydraulic elevator. Each time movement of an elevator car is commanded, then the starter must start the motor until it reaches operating speed and then operate in a run mode. Such a starter may only be used for the up direction as gravity may be used for the down direction.
One type of elevator starter, referred to as a soft starter, changes the on time of the solid state switches to control voltage and to ramp up motor current with a fixed connection. The soft starter may use a fault contactor to open the path for current to flow to the motor in instances where the soft starter might fail, such as a shorted SCR condition. However, there may be instances where the fault contactor control coil is not wired properly, which could result in a condition where the fault contactor does not open in a fault condition. This could result in a damaged motor. Another condition that may cause the contactor to remain in the on state could be welded contacts in the fault contactor or in the elevator control system.
The present invention is directed to solving one or more of the problems discussed above, in a novel and simple manner.